In urban high-rise buildings constructed of concrete and steel, traditional public safety communications systems such as police and fire radio systems as well as cellular radio systems are often unable to effectively receive or transmit voice and data communications throughout the building from radio sources outside the building. Typical dead zones include stairwells and other similar spaces that are enclosed on all sides by steel reinforced structure. The existence of wireless “dead zones” in a communications network can have fatal consequences when there is a fire or other emergency condition within the building and emergency personal within the building cannot be contacted.
The Sep. 11, 2001 attacks on the World Trade Center in New York City and the resulting deaths of civilians and emergency personnel are a particular example of the problems with a deficient communications infrastructure. Point to point communications systems were not able to meet the challenges of maintaining communications between a command station at the base of a building with fire crews that were 50 stories up in the structure. As a result, many jurisdictions have enacted ordinances that require new and retrofitted commercial buildings to install systems that ensure radio coverage for public safety signals within the building as a condition of occupancy. Nationwide model codes have been developed that address public safety for in-building communications.
As one example, the New York City Building Code requires, in Sections 403.4.4 and 907.2.13.2, that an in-building auxiliary radio communication (ARC) system be installed and maintained in all newly-constructed high-rise buildings. An ARC system is a wireless two-way building communication system for Fire Department use only that receives and transmits Fire Department portable radio frequencies within the building. An ARC system will typically include a transceiver (e.g., a base station) connected to a building-wide distributed antenna system, with a radio console in the building lobby. Section 917.1.2 of the New York City Building Code and Section FC 511 of the New York City Fire Code together require that ARC systems be installed, that they be tested, and that they be operated and maintained in accordance with the Fire Code and the rules of the Fire Department.
These improvements in the implementation and, very importantly the monitoring of these systems provide a significant benefit to the robustness of hand held wireless communication systems. However, it has been determined that it is common to have installed ARC cables and components damaged for example, during construction and renovation. Without proper monitoring, damage to the ARC system could go unnoticed causing communications disruptions within the structure, increasing the potential for serious injury or death when that system was required during an emergency.
The Fire Department of New York City mandated new rules for ARC systems that require periodic monitoring of all the elements of a Radio Frequency Distributed Antenna System (RF-DAS). The requirements provide that, while in standby, the RF-DAS should perform a periodic self-test to assure proper performance when the system is needed in an actual emergency. Fire Department rules also establish requirements for the design, installation, operation and maintenance of ARC systems. These rules include testing procedures necessary to confirm that the ARC system is providing adequate radio coverage in the building in all areas accessible for firefighting operations. The rules seek to ensure that ARC systems achieve their intended purpose and, once installed, are continuously maintained in good working order.
One system that has sought to ensure the proper functioning of the distributed antenna system throughout a structure is U.S. Pat. No. 7,224,170 entitled “Fault Monitoring in a Distributed Antenna System.” The '170 patent describes a central monitoring unit and a plurality of antennas coupled to the central monitoring unit through a network. Each antenna includes an antenna monitoring unit, which determines whether the associated antenna is properly connected to the network. To accomplish this, the antenna monitoring unit includes a measurement circuit for measuring a current drawn by its associated antenna and a reporting component for outputting a status message to the central monitoring unit. The current drawn by the antenna is measured and compared against a reference level. The measured level of current drawn by the antenna is indicative of whether the antenna is properly connected.
However, the '170 patent teaches use of a system where the fault monitoring communication path to the antenna network is not isolated from the antenna signal path. For example, with reference to FIG. 2 the antenna is directly connected to the main signal line and extends to the “Wireless Base Station.” There is no DC isolation of the antenna to the central monitoring unit. While the '170 patent discloses that two-way communication to the antenna monitoring unit 22 is possible, it teaches that the communication is in the form of “low frequency signals.” The '170 patent then goes on to broadly state that the system could include system “which carry RF and status signal, in digital or analog format.” However, the monitoring circuit in '170 is not capable of using a digital signal to transmit information due to the lack of any DC isolation of the antenna. Additionally, with reference to FIG. 2, the '170 patent is focused on a grounded type antenna.
As stated above, the '170 patent uses “low frequency signals.” As a design requirement, diagnostic monitoring of the RF-DAS system cannot emit RF signals in the already RF noisy urban environment. Additionally, the monitoring should be able to locate any non-functioning elements, right to and including the antenna itself. The system should use the RF Transmission lines and not require other external wires or wireless devices.